As set forth in U.S. Pat. No. 4,102,704 (Fournier et al.), it is well known to incorporate modified or unmodified resins or rosins to improve the characteristics of pigmentary compositions intended for use in printing inks.
In general, suitable additives include natural and synthetic resins. Rosin, often referred to as colophony, disproportioned rosin, hydrogenated rosin, and rosin derivatives are preferred resins for the present purposes. Such rosins have high compatibility with the binding agents employed in printing inks, have low softening points, as well as being soluble in an aqueous alkaline medium and substantially insoluble in an acidic medium.
Organic pigments are generally resinated or rosinated during or after the conventional coupling procedure to achieve better dispersion of the pigmentary particles resulting in increased strength, transparency, and depth of mass tone for the pigments. The resin or rosin is normally precipitated as free acid or as a metal salt of calcium, barium or zirconium. In U.S. Pat. No. 4,102,704, column 1, lines 26 through 35; French Pat. No. 1,538,270 and Belgian Pat. No. 660,978 are referred to for the foregoing teachings as well as the use of organic amines to react with the resin or rosin. Furthermore, the use of small quantities of wetting agents such as the oleic ester of triethanolamine is taught. The use of these additives are said to have the disadvantage of causing a loss in coloristic intensity.
The disadvantages of the prior art procedures are said to be overcome in U.S. Pat. No, 4,102,704 by incorporating modified or unmodified resin acids esterified with an amino alcohol in an acid aqueous solution containing the organic pigment. The esters are then precipitated by making the aqueous solution alkaline or by adding an acid which will form water insoluble salts. One of the features of the patented invention involves preparing the esters of the resin acids in a separate step.
Somewhat more recently, Canadian Pat. No. 1,170,802 proposes utilizing a high percentage of resin or rosin precipitated on the organic pigment as free acid to achieve high transparency and high tinctorial strength. However, when the manufacturing method of the Canadian Patent was utilized, for example, with a C.I. Pigment Yellow-12, and in conjunction with a flushing treatment, the resulting flush had low viscosity and consequently needed more gelled vehicles to build up yield values for the ink so that it in turn would print better.
It would be advantageous therefore to have available a method for making pigmentary compositions that avoided such prior art problems or commercial problems as additional processing steps, loss of color intensity, and undesirable viscosities when incorporated into ink. The product obtained by the practice of the method should lead to high strength, better transparency, and good rheological characteristics when used in printing inks.